Java多线程之可见性与原子性——synchronized VS volatile

<转：http://blog.csdn.net/uniquewonderq/article/details/48113071>

 

程序举例：

代码：

package com.synch;
public class SynchronizedDemo {
    //共享变量
    private boolean ready = false;
    private int result = 0;
    private int number = 1;
    //写操作
    public synchronized void write(){
        ready = true;
        number = 2;
    }
    //读操作
    public synchronized void read(){
        if(ready){
            result = number*3;
        }
        System.out.println("result的值为：" + result);
    }

    //内部线程类
    private class ReadWriteThread extends Thread {
        //根据构造方法中传入的flag参数，确定线程执行读操作还是写操作
        private boolean flag;
        public ReadWriteThread(boolean flag){
            this.flag = flag;
        }
        @Override
        public void run() {
            if(flag){
                //构造方法中传入true，执行写操作
                write();
            }else{
                //构造方法中传入false，执行读操作
                read();
            }
        }
    }

    public static void main(String[] args)  {
        SynchronizedDemo synDemo = new SynchronizedDemo();
        //启动线程执行写操作
        synDemo .new ReadWriteThread(true).start();
//      try {
//          Thread.sleep(1000);
//      } catch (InterruptedException e) {
//          // TODO Auto-generated catch block
//          e.printStackTrace();
//      }
        //启动线程执行读操作
        synDemo.new ReadWriteThread(false).start();
    }
}

代码示例：

package com.synch;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class VolatileDemo {

    private Lock lock = new ReentrantLock();
    private int number = 0;

    public int getNumber(){
        return this.number;
    }

    public void increase(){
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        lock.lock();
        try {
            this.number++;
        } finally {
            lock.unlock();
        }
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        final VolatileDemo volDemo = new VolatileDemo();
        for(int i = 0 ; i < 500 ; i++){
            new Thread(new Runnable() {

                @Override
                public void run() {
                    volDemo.increase();
                }
            }).start();
        }

        //如果还有子线程在运行，主线程就让出CPU资源，
        //直到所有的子线程都运行完了，主线程再继续往下执行
        while(Thread.activeCount() > 1){//让所有的子线程都执行完后，然后再执行<pre name="code" class="java">//System.out.println("number : " + volDemo.getNumber());   语句。因为主线程算一个。当活跃线程为1时，也就是所有的子线程执行完毕了。此///时退出while 循环执行输出语句。

Thread.yield();}System.out.println("number : " + volDemo.getNumber());}}